Heating solution for H bridge transistor circuits

I want to talk about one of the major cause of heating in  H bridge and half bridge circuits which finally leads to failure. Though transistors in H bridge or half bridge may fail for many reasons, the most common cause of failure is "NO or SHORT DEAD TIME".

 DEAD TIME OF H BRIDGE CIRCUIT

From the theory behind H bridge mosfets or H bridge transistor circuits, power is delivered to the load when two diagonal transistors turns on. That is either (B and C ) or (A and D) from the image above.

The H bridge circuit is divided into two sides: Left side and right side. One of the principles guarding all H bridge circuits is that:
NO TRANSISTORS FROM THE SAME SIDE SHOULD TURN ON AT THE SAME TIME. Eg. A and C  or B and D.

When transistors from same side turns on, a phenomenon called shoot through will occur and that will produce a blasting sound, nice smell and  beautiful smoke.

In order to avoid shoot through, H bridge and half bridge circuit should be driven in such a way that, transistors from same side does not turn on and also transistors are only turn on diagonally.

In other to ensure that transistors are turned on only diagonally,  a small delay time known as dead time is introduced in the switching circuit. The delay circuit is ensures that one diagonal switch side is completely turned off before the next diagonal turns on.

Heating solution for H bridge transistor circuits

 Heating in H bridge transistor as a result no or short dead time can be solved by

 

 

H BRIDGE

H Bridge circuit is the arrangement of electronic switches in a pattern that forms the letter ''H'' during switching. The switches may be bipolar transistors, Mosfets, IGBTs, etc. 

These switches are controlled by logic signals in such a way that the four arranged switched connected in "H" turns on diagonally as shown below:

In H bridge circuit, never should two switches on the same side eg. A and C or B and D be turned on at the same time.

Turning A and B or C and D on at the same time will create a bombing sound and all your mosfets or transistor will produce beautiful smoke with a nice smell......Hahaha

H BRIDGE CIRCUIT FOR INVERTERS

In inverter systems, H bridges are mostly used for pure sine inverters with only few modified sine wave inverters using them.

H bridge inverters are best for me especially when it comes to their way of charging your batteries until float level. The circuit below is an H bridge circuit which can handle 1000W to 3000W 12V, 1000W to 4000W 24V, 1000W to 5000W 48V.  

Before you use any mosfet, please make sure your highest switching voltage is less than the maximum operating voltage of your mosfets by at least half. 

Example 48V inverters should use at least 100V mosfets using 75V may result in failure.

H BRIDGE DRIVER CIRCUIT

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NB. without the addition of surge capacitors or not adding enough, your pure sine inverter will fail on inductive loads eg. fridges, air conditioners etc.

You can assume that 10000uf is for every 1000W.

There is something I omitted, that is a fast switching diode paralleled with a 47ohms resistor to feed the high sides and the low sides gates. 

Connect this in series to the output of your driver stage before connecting it to this H bridge. Its another form of protection against failure. 
Read more about this by clicking this link
http://manycircuits.blogspot.com/2017/05/mosfet-heating-solution-for-h-bridge.html

Types of inveter protection

Inverters must have various protections so that they can withstand the tests of time. At times, the inverters you design or build are not used by only you. Therefore its advisable to include some basic decision making functions for the inverter to behave at every point as though you are making those decision at those points in time.

Below are some basic inverter protections which can be achieve by using op amps configured as comparators. If you are into programing, you can also include them in your programs, else its advisable to use op amps. 

 INVERTER PROTECTIONS

• Overload warning alarm with indicator
  

• Overload shutdown

• Low battery alarm

• Low battery shutdown

• Over temperature protection with indicator

• Over battery protection

• Float charging system

• Temperature based fan control

INVERTER PROTECTIONS FUNCTIONS EXPLAINATION

•    Overload warning alarm with indicator: This function monitors the amount of load powered by the inverter.  When the total load connected to the inverter reaches 90% of the rated inverter system, the system alarm triggers with an indicator on. This prompts the user that He or She is about to overload the system.

• Overload shutdown: This function takes care of overloads and short circuit instances. When overload or short circuit occurs, this function turns off the inverter output to protect the inverter from damage.

• Low battery alarm and shutdown: This function takes care of battery protection. It is always good to ensure that, the battery of an inverter is not deeply drain to prolong the battery life. During inverter usage, this function monitors the battery level and triggers the system alarm when the battery level reaches a set level. After the alarm, the inverter turns off to protect the battery from over draining.

•  Over temperature protection with indicator: Every electronic system as well as inverters produces some amount of heat as a result energy conversion and power loss. But this heat should always be in an acceptable level to ensure high efficiency and avoidance of failure.

    The over temperature protection system monitors the system temperature and turn system function (charging or working as inverter) off when system temperature is above acceptable level which is a sign of possible problem.

• Over battery protection: This function is included to ensure that, if a customer buys the inverter and uses the wrong number of batteries (uses 24V instead of 12V), the system will never turn on until the correct battery system is used.

• Float charging system: When this charging technique is employed in designing, it ensures that the batteries are always charged without ever overcharging them.

• Temperature based fan control: The system fan should be designed to turn on only when the system begins to gain heat and turn off after extracting the heat. This function ensures that the inverter system is always silent.

fan control circuit

Automatic temperature controlled fan using NTC.
Sometimes, the systems that removes the heat can be disturbing with its noise. I want to show you a simple circuit that will remove heat from your electronic gadgets and systems that produces heat.

The advantage of this circuit is that, the fan only turns on when there is heat in the system and turns off after removing that heat.

Automatic  fan control circuit

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Simple automatic change over circuit

Simple automatic change over circuit for homes and work places.

Change overs are required whenever you are handling two or more power from different sources. In homes where inverters or generators are stand by power sources, it is advisable to use a change over system so that when your stand by power is in use, power will not flow into your national power supply.

Also, when change overs are not installed, power will run into your stand by source and destroy it. If its an inverter, all the output mosfets will blow up and even catch fire. Generators may also explode when that happens.

Change overs can be manual or automatic. With manual change overs, u have to wake up from your sleep to change over when your nation grid goes off or when your national grid is restored. Automatic change overs on the other hand does every switching automatically and even connect your inverter for charging.

The circuit is an automatic change over circuit with delay of 20 to 50 seconds, power restored notification alarm and charging port for those who will be using it for inverters.

The circuit is based on 555 timer IC, 220V Contactor, 12V relay, a buzzer, a transformer and few resistors and capacitors.

AUTOMATIC CHANGE OVER CIRCUIT FOR INVERTERS AND GENERATORS

HOW TO DOUBLE TRANSFORMER VOLTAGE

A circuit to double or step up the output of a small transformer so that it can power high voltage circuits. High voltages are at times needed but its a problem when we have to spend huge sums of money before we accomplish it.

Am going to show you a high current circuit which can double or even triple the output of any transformer connected to it. The circuit can be used as car battery chargers, inverter battery chargers and as a regular power supply. 

TRANSFORMER BOOST CIRCUIT FOR POWER SUPPLY AND CHARGERS

 

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AUTOMATIC SWICH CIRCUIT

Switch circuit which saves energy consumption by automatically turning off appliances connected to it either at day or at night. This switch circuit can be employed to reduce the energy consumption of fridges, air conditioners, lights, and many more appliances that you want to control their turn on time.

The circuit is based on light dependent resistor (LDR) popularly known as photo cell. The LDR is a type of resistor which reduces its resistance when light falls on it. The resistance value is directly proportional to the amount of light that falls on it. The more the light, the less the resistance of the LDR and the less the light, the high the resistance.

In this circuit, the LDR is our sensor which controls the relay U1 and also your connected load..

AUTOMATIC SWITCH CIRCUIT